The invention relates generally to ignition systems. More particularly, the invention relates to ignition systems that use gated switches for controlling energy discharge to a plurality of igniters.
Conventional ignition systems typically include one or more igniters through which energy is discharged from an energy storage device such as a capacitor. The discharge is characterized by a high current/voltage spark or plasma that occurs due to high voltage breakdown across the igniter gap, including air gap and semiconductor gap igniter plugs.
A conventional ignition system for an internal combustion engine, such as, for example, a gas turbine aircraft engine, includes a charging circuit, a storage capacitor, a discharge circuit and at least one igniter plug located in the combustion chamber. The discharge circuit includes a switching device connected in series between the capacitor and the plug. For many years, such ignition systems have used spark gaps as the switching device to isolate the storage capacitor from the plug. When the voltage on the capacitor reaches the spark gap break over voltage, the capacitor discharges through the plug and a spark is produced. More recently, solid state switches such as SCR, GTO and MCT devices have been investigated.
It is generally known that energy levels from multiple storage means can be combined to increase discharge energy through a single igniter. It is also known that a single energy storage source can be multiplexed to produce sparks in a plurality of igniters, such as shown in U.S. Pat. No. 3,880,132 issued to Whatley. However, this arrangement is unsuitable for applications such as gas turbine engine ignition systems because the use of a single pulse forming (wave shaping) network can overstress solid state gated switches. In another arrangement, such as shown in U.S. Pat. No. 3,605,704 issued to Hardin, a single capacitor is used to produce sparks in multiple plugs including the use of separate pulse shaping networks to reduce stress on the switches, such as might be used in a spark distribution system that fires each plug at a rate proportional to engine speed. However, this system is unsuitable for aerospace applications wherein discharge energy and spark rates need to be controlled based on factors other than engine speed, such as igniter wear, temperature, fuel mix, and turbulence, for example.
The need exists, therefore, for an ignition or spark discharge system that can produce different energy level discharges to selectable igniters, as well as at different spark rates. Particularly needed is such a system that can be adapted for use with gas turbine engines, such as used in aircraft applications.